Chemical evolution of gas and solids in protoplanetary disks
Kenji Furuya (NAOJ)
Planets form in protoplanetary disks. Understanding the chemical evolution of disk materials (gas and solids) is thus the essential first step to understand how planets acquire their compositions. Chemical evolution of disks has been investigated for many years using numerical simulations, but the effect of dust evolution has been mostly ignored. We recently developed a coupled physical and chemical model, in which coagulation and radial drift of dust grains and chemical reactions in gas and solid phases are considered in a self-consistent manner. We find that disk chemical evolution is largely set by the radial drift of ice-mantled dust grains, sublimation of ices, and the chemical conversion of CO into less volatile molecules, such as CO2 and hydrocarbons. We also find that there are two requirements to explain the low CO abundance observed in the TW Hya disk: low threshold fragmentation velocity (~1 m/s) and the cosmic-ray ionization rate similar to the level in the dense ISM.